Highly Optimized Digital IQ Transmitter Chain

ABSTRACT

Circuitry separates a modulation signal into digital sign and magnitude signal components. The digital magnitude signal is converted to an analog magnitude signal. The analog magnitude signal is the mixed with an in-phase or quadrature carrier signal under the influence of the digital sign signal and routed to a driver output stage.

BACKGROUND

System-on-chip (SoC) integration on CMOS within wireless systems, inconjunction with the ongoing CMOS shrinkage path, requires appreciableredesign in order to accommodate industry goals. This is especially truefor radio frequency (RF) and some analog devices. The result of thecontinuous march toward integration and miniaturization is thatarchitectures require increased digital circuitry and a reduction inpurely analog sub-systems.

Multi-modal radios and other wireless devices present their ownchallenges in regard to the foregoing paradigm. In particular,respective developments for receivers, synthesizers and transmitters areneeded to optimize overall system design. Additional goals in thisregard include area savings and reduced current and power consumption.In short, improved SoC design is desirable as applied to wireless andother devices.

Illustrative Background Structures

FIG. 1 shows a transmitter structure (transmitter) 100 in accordancewith known techniques. The transmitter 100 shows one approach usingpolar modulator architecture. The structure 100 includesin-phase-and-quadrature (IQ) to polar conversion circuitry (i.e., or asub-system) 102. The IQ subsystem 102 receives an in-phase modulation(i.e., intelligence) signal at an input 104 and a quadrature modulationsignal at an input 106. The in-phase and quadrature modulation signalsare understood to be orthogonal to one another. The IQ subsystem 102 iscapable of deriving distinct phase (i.e., angular degrees) and magnitude(i.e., absolute value) signals from the in-phase and quadraturemodulation signals. An illustrative magnitude signal S1 is depicted inFIG. 1. Such derived phase-and-magnitude representation of modulationsignals is also referred to as polar modulation.

Once the IQ subsystem (i.e., polar modulator) 102 derives the phase andmagnitude signals, the phase information is modulated onto a carriersignal 108 by way of time derivative function block 110 and adder 112. Adigital phase-lock loop (PLL) 114, being controllably influenced by themodulated carrier signal from adder 112, in turn controls an analoglocal oscillator (LO) 116. The LO 116 output signal is input to an IQgenerator 118, which serves to provide in-phase and quadrature signalscorresponding to the modulated carrier signal. Herein, the differencebetween such in-phase and quadrature signals is generally referred to asa differential signal.

The transmitter 100 also includes a digital-to-analog converter (DAC)120. The DAC 120 is configured to receive the magnitude signal from theIQ subsystem 102, in digital signal form, and derive a correspondinganalog magnitude signal. The analog magnitude signal and thedifferential signal are mixed at a mixer 122, power amplified by adriver 124 and coupled to one or more antennas 126.

It is noted that within the architecture of transmitter 100, themagnitude (i.e., amplitude) signal S1 is introduced directly to themixer 122 prior to the driver (i.e., final amplifier) 124 stage. Underthis polar modulation structure, especially for a digitalimplementation, the magnitude signal is always positive (i.e., ofconsistent polarity) and therefore the current through the mixer (e.g.,the mixer 122) is changing with the magnitude without using a steadyD.C. (direct current) current draw. This situation corresponds,generally, to class-B operation and shows favorable efficiency.

One challenge in using polar modulation architecture is establishing andmaintaining proper synchronism between the phase and magnitude signals.This challenge is becoming more daunting as modulation bandwidths (i.e.,information content per unit time) continue to increase in the industry.Illustrative narrowband systems like GSM and Bluetooth are such thatpolar modulation can be effectively applied without huge efforts.However, other protocols such as W-CDMA (i.e., Wideband Code DivisionMultiple Access) have requirements that are difficult to achieve. Othersystem protocols, such as WLAN (i.e., Wireless Local Area Network—IEEE802.11 standard) or WiMax, have a bandwidth greater than 5 MHz and therespective requirements are extremely difficult to fulfill in massproduction or necessitate incredible alignment efforts.

FIG. 2 shows another transmitter 200 in accordance with knowntechniques. The transmitter 200 includes functional elements (i.e.,circuits, or sub-systems) that are analogous to respective elementswithin the transmitter 100, including a digital phase-lock loop 214, alocal oscillator 216, and an IQ generator 218. Transmitter 200 furtherincludes in-phase input node 204 and quadrature input node 206,respectively coupled to in-phase modulation signal S2 and quadraturemodulation signal S3.

However, transmitter 200 does not include a polar modulator as wasutilized by transmitter 100. Rather, transmitter 200 includes respectiveDACs 210 and 212. The DAC 210 is configured to receive the in-phasemodulation signal from node 204, in digital signal form, and derive acorresponding analog in-phase signal. The analog in-phase signal fromthe DAC 210 is then mixed with a differential signal provided by the IQgenerator 218 using a mixer 220. The mixed signal from mixer 220 is thenrouted to an adder 222.

In turn, the DAC 212 is configured to receive the quadrature modulationsignal from node 206, in digital signal form, and derive a correspondinganalog quadrature signal. The analog quadrature signal from the DAC 212is then mixed with the differential signal provided by the IQ generator218 using a mixer 224. The mixed signal from mixer 224 is then routed tothe adder 222, where it is summed with the other mixed signal from mixer220 to define a summation signal. The summation signal is then poweramplified by a driver 226 and routed to at least one antenna 228.

The transmitter 200 of FIG. 2 utilizes what is referred to as IQmodulation, by virtue of the separate digital-to-analog conversion ofboth the in-phase and quadrature modulation signals (S2 and S3). IQmodulation is preferred in instances where high modulation bandwidth isto be achieved. However, disadvantages regarding implementation andefficiency under IQ modulation stem from the fact that the in-phase andquadrature modulation signals span respective value ranges having bothpositive and negative values (i.e., signal polarities). Thus, within anIQ modulation context, the DAC stages require sufficient circuitcomplexity and operating speed to convert bi-polar input signals. Suchrequirements can be difficult to achieve, particularly in a massproduction environment.

Presently, the most readily employed IQ modulation structures,particularly in a digital implementation, add certain predefined offsets(i.e., biases) before or after the analog-to-digital conversion stagewithin the respective in-phase and quadrature signal flow paths. Anundesirable consequence of this approach is that the advantages andspeed of class-B operation no longer exist.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.

FIG. 1 is a block diagram of a transmitter structure in accordance withknown techniques.

FIG. 2 is a block diagram of another transmitter in accordance withknown techniques.

FIG. 3 a block diagram depicting a transmitter structure in accordancewith the present teachings.

FIG. 4 is a block schematic diagram depicting electronic circuitry inaccordance with the present teachings.

FIG. 5 is a block schematic diagram depicting electronic circuitry inaccordance with the present teachings.

FIG. 6 is a block schematic diagram depicting electronic circuitry inaccordance with the present teachings.

FIG. 7 is a flow diagram depicting a method in accordance with thepresent teachings.

DETAILED DESCRIPTION

Disclosed herein are circuits for use with wireless systems. Accordingto one implementation, an electronic circuit separates a digitalmodulation signal into a digital sign signal and a digital magnitudesignal. A digital-to-analog converter converts the digital magnitudesignal into an analog magnitude signal. A mixer then mixes at least theanalog in-phase magnitude signal and the digital in phase sign signal toprovide a mixed signal.

According to another implementation, an electronic circuit includeselements configured to define a digital-to-analog converter (DAC). TheDAC is configured to perform responsive to a multi-state switchingsignal and an in-phase and quadrature (IQ) differential signal. Thecircuitry further includes elements cooperatively configured to define amixer. The mixer receives signals from the DAC, and performs mixingresponsive to a digital sign signal. The mixer couples the mixed signalto a pair of output nodes.

According to still another implementation, an electronic circuitincludes elements cooperatively configured to define a digital-to-analogconverter (DAC). The DAC is configured to perform responsive to amulti-state switching signal and an in-phase and quadrature (IQ)differential signal. The circuit also includes respective elementscooperatively configured to define a mixer. The mixer receives signalsfrom the DAC and performs responsive to a digital sign signal and aninverted form of the digital sign signal. The mixer is configured toprovide a mixed signal by way of a pair of output nodes.

In yet another implementation, an electronic circuit includes elementscooperatively configured to define a digital-to-analog converter (DAC).The DAC is configured to perform responsive to a multi-state switchingsignal, and first and second multiplexed signals. The electronic circuitalso includes respective elements cooperatively configured to define abuffer, the buffer coupled to receive signals from the DAC to a pair ofoutput nodes, the buffer configured to perform responsive to a constantreference voltage.

In another implementation, a method includes separating a digitalmodulation signal into a digital sign signal and a digital magnitudesignal. The method also includes converting the digital magnitude signalto an analog magnitude signal. The method further includes mixing atleast the analog magnitude signal and the digital sign signal to derivea mixed signal.

Circuit structures provided herein can be fabricated, at least in part,on a common substrate such that respective integrated circuit devicesare defined. In one or more implementations, at least a portion of drivecircuits presented herein can be fabricated within a 65 nanometer (orsmaller) environment.

The techniques described herein may be implemented in a number of ways.One illustrative context is provided below with reference to theincluded figures and ongoing discussion.

First Illustrative Implementation

FIG. 3 depicts an illustrative transmitter structure 300 in accordancewith one implementation of the present teachings. The transmitter 300may be a portion of a transceiver in one or more implementations. Thetransmitter 300 includes a carrier signal input 302 coupled to a digitalphase-lock loop (D-PLL) 304. The D-PLL 304 controls a local oscillator(LO) 306 that provides an input signal to an IQ generator 308. The IQgenerator 308, in response to the LO 306 signal, provides an in-phasecarrier signal (IC) and a quadrature carrier signal (QC), wherein thedifference between these two signals is referred to as a differentialsignal (DS). In this way, the differential signal DS produced by the IQgenerator 308 corresponds to the carrier signal received at input 302.

The transmitter 300 also includes in-phase modulation signal input 310and quadrature modulation signal input 312. Circuitry 314 derives adigital in-phase sign signal S4 from the in-phase modulation signal. Inturn, circuitry 316 derives a digital in-phase magnitude signal S5 fromthe in-phase modulation signal. Additionally, circuitry 318 derives adigital quadrature magnitude signal S6 from the quadrature modulationsignal, while circuitry 320 derives a digital quadrature sign signal S7from the quadrature modulation signal.

The transmitter 300 also includes a digital-to-analog converter (DAC)322. The DAC 322 receives the digital in-phase magnitude signal S5 fromcircuitry 316 and derives an analog in-phase magnitude signal. Theanalog in-phase magnitude signal is then mixed with the in-phase carriersignal IC from the IQ generator 308, and the digital in-phase signsignal S4, using a mixer 324 so as to derive a mixed signal.

The transmitter 300 further includes another digital-to-analog converter(DAC) 326. The DAC 326 receives the digital quadrature magnitude signalS6 from circuitry 318 and derives a corresponding analog quadraturemagnitude signal. This analog quadrature magnitude signal is then mixedwith the quadrature carrier signal QC from the IQ generator 308, and thedigital in-phase sign signal S7, using a mixer 328 to derive anothermixed signal. Both of the mixed signals—from mixers 324 and 328,respectively—are coupled to an adder 330. The adder 330 sums the twomixed signals and provides a summation signal to a driver 332, which inturn drives one or more antennas 334.

The transmitter 300 bases its operation on the separation of sign andmagnitude information (i.e., signals) from the respective in-phase andquadrature modulation signal inputs (at 310 and 312). Thereafter,representative sign (digital) and magnitude (analog) signals arerecombined at respective mixer stages (324 and 328), along with in-phase(IC) and quadrature (QC) signals corresponding to the carrier wave. Inthis way, transmitter 300 assures that only positive (i.e., singlepolarity) signals are input to, and converted by, the respective DACs322 and 326. Furthermore, the transmitter 300 exhibits class-B operation(or nearly so) at the driver stage 332, thus performing with desirableefficiency and overall operating speed.

Second Illustrative Implementation

FIG. 4 is a block schematic diagram depicting electronic circuitry(i.e., circuitry) 400 in accordance with the present teachings. Onehaving ordinary skill in the pertinent arts can appreciate that otherfunctional elements respectively taught herein and/or known in the artcan be used in combination with the electronic circuitry 400. However,such other functional elements are omitted from FIG. 4 in the interestof simplicity and clarity of understanding.

The circuitry 400 includes circuitry (i.e., functional block) 402configured to receive either a digital in-phase or digital quadraturemodulation signal from input 404. In turn, the block 402 derives (i.e.,provides) a digital sign signal and an inverted form of the digital signsignal, in accordance with the instantaneous polarity of the inputmodulation signal. The circuitry 400 also includes other circuitry(i.e., another functional block) 406 configured to receive the samedigital in-phase or digital quadrature modulation signal from input 404.In turn, the functional block 406 derives (i.e., provides) a digitalmagnitude signal corresponding to the input modulation signal.

The circuitry 400 also includes an IQ generator 408 configured toreceive a carrier signal from a local oscillator (not shown; refer to306 of FIG. 3) and to provide an analog in-phase carrier signal and ananalog quadrature carrier signals. The difference between the in-phaseand quadrature carrier signals is referred to as a (analog) differentialsignal DS1.

The circuitry 400 includes a multiplexer (MUX) 410. The MUX 410 isconfigured to receive the digital magnitude signal from block 406, theinverted digital sign signal from block 402, and a logic level ‘zero’reference signal. The MUX 410 is further configured to provide amulti-state switching signal SS1 corresponding to a predeterminedfunction of the magnitude, logic zero, and inverted sign input signals.As such, the MUX 410 can be considered to be a state machine havingthree input signals and one multi-state output signal. Furtherelaboration regarding the MUX 410 and the signal SS1 is providedhereinafter.

The circuitry 400 further includes another multiplexer (MUX) 412. TheMUX 412 is configured to receive the digital magnitude signal from block406, the digital sign signal from block 402, and the logic level ‘zero’reference signal. The MUX 412 is further configured to provide amulti-state switching signal SS2 corresponding to a predeterminedfunction of the magnitude, logic zero and sign input signals. As such,the MUX 412 can also be considered to be a state machine having threeinput signals and one multi-state output signal.

The circuitry 400 also includes a first transistor 414, a secondtransistor 416, and a plurality of selectably switchable current sources(current sources) 418. The transistors 414 and 416 and the plurality ofcurrent sources 418 cooperatively define a digital-to-analog converterDAC1. That is, elements 414, 416 and 418 collectively function so as toprovide digital-to-analog signal conversion. The DAC1 is configured toderive an analog magnitude signal corresponding to the digital magnitudesignal from block 406, under the controlling influence of differentialsignal DS1 and the multi-state switching signal SS1.

Each of the current sources 418 can be configured to provide anyrespectively suitable current value. In one non-limiting implementation,all of the current sources 418 are configured to provide a commonelectrical current value (e.g., all provide 0.01 mA, etc.). In anothernon-limiting implementation, the current sources 418 are respectivelyconfigured to provide unique electrical currents such that the overallplurality exhibits constant steps therebetween (e.g., one current sourceat each of 0.01 mA, 0.02 mA, 0.03 mA . . . , etc.). Other weightingschemes can also be used (linear weighting, binary weighting,logarithmic weighting, etc.). Thus, the current sources 418 can beindividually weighted so that, through selective switching, anypractical combination of electrical currents can be summed at node 420.In any case, the selective switching of current sources 418 to the node420 is accomplished by way of the multi-state switching signal SS1.While a total of three current sources 418 are depicted, it is to beunderstood that any suitable number of current sources 418 can beincluded in accordance with the resolution of the signal conversion tobe performed by DAC1.

The circuitry 400 also includes a third transistor 422 and a fourthtransistor 424 cooperatively configured to define a mixer MIX1. Themixer MIX1 is configured to mix the analog magnitude signal provided byDAC1 with the digital sign signal and inverted digital sign signalprovided by block 402. The mixer MIX1 then provides the resulting mixedsignal to a pair of nodes 426.

The circuitry 400 also includes a fifth transistor 428, a sixthtransistor 430, and another plurality of selectably switchable currentsources (current sources) 432. The transistors 428 and 430 and theplurality of current sources 432 cooperatively define anotherdigital-to-analog converter DAC2. Thus, elements 428, 430 and 432collectively function so as to provide digital-to-analog signalconversion. The DAC2 is configured to derive an analog magnitude signalcorresponding to the digital magnitude signal from block 406, under thecontrolling influence of differential signal DS1 and the multi-stateswitching signal SS2.

Each of the selectable current sources 432 can be defined to provide anyrespectively suitable current value. As such, any suitable weightingscheme can be used (linear weighting, binary weighting, logarithmicweighting, etc.). Thus, the current sources 432 can be individuallyweighted so that, through selective switching, any practical combinationof electrical currents can be summed at node 434. The selectiveswitching of current sources 432 to the node 434 is accomplished by wayof the multi-state switching signal SS2. While a total of three currentsources 432 are depicted, it is to be understood that any suitablenumber of current sources 432 can be included in accordance with theresolution of the signal conversion to be performed by DAC2.

The circuitry 400 further includes a seventh transistor 436 and aneighth transistor 438 cooperatively configured to define a mixer MIX2.The mixer MIX2 is configured to mix the analog magnitude signal providedby DAC2 with the digital sign signal and inverted digital sign signalprovided by block 402. The mixer MIX2 then provides the resulting mixedsignal to the pair of nodes 426. The nodes 426 are coupled to the sourceof bias potential V-BIAS by way of respective resistors 440 and 442. Thenodes 426—also referred to as output nodes—are understood to be coupledor coupleable to a driver or other suitable stage (e.g., driver 332 ofFIG. 3).

In operation, the circuitry 400 cross-switches between independentstages, wherein stage 1 includes DAC1 and MIX1, and stage 2 includesDAC2 and MIX2, respectively. Such cross-switching between stages 1 and 2is performed in accordance with the assertion of the digital sign signalor inverted form of the digital sign signal, respectively. Specifically,when the sign signal provided by block 402 is asserted, then the mixedsignal provided by MIX1 is routed to node pair 426. Conversely, when theinverted form of the sign signal provided by block 402 is asserted, thenthe mixed signal provide by MIX2 is coupled to node pair 426. In otherwords, an assertion of either the sign signal or the inverted form ofthe sign signal determines which the two stages is active any particularinstant. In this way, the circuitry 400 handles both positive andnegative polarities of the input modulation signal at node 404, whilefacilitating class-B operation (or nearly so) at the output signaldriver stage (not shown).

The circuitry 400 can be implemented in any number of suitableimplementations. In one non-limiting implementation, some or all of thecircuitry 400 can be implemented as an integrated circuit. In anothernon-limiting implementation, some or all of the circuitry 400 can beimplemented within a 65 nanometer environment. In yet anothernon-limiting implementation, some or all of the circuitry 400 isimplemented via one or more discrete electronic components. Otherimplementations of the circuitry 400, or a portion thereof, can also beused.

Third Illustrative Implementation

FIG. 5 is a block schematic diagram depicting electronic circuitry(i.e., circuitry) 500 in accordance with the present teachings. Onehaving ordinary skill in the pertinent arts can appreciate that otherfunctional elements respectively taught herein and/or known in the artcan be used in combination with the electronic circuitry 500. However,such other functional elements are omitted from FIG. 5 in the interestof simplicity and clarity of understanding.

The circuitry 500 includes circuitry (i.e., functional block) 502configured to receive either a digital in-phase modulation signal or adigital quadrature modulation signal from input 504. In turn, the block502 derives (i.e., provides) a digital sign signal and an inverted formof the digital sign signal, in accordance with the instantaneouspolarity of the input modulation signal. The circuitry 500 also includesother circuitry (i.e., another functional block) 506 configured toreceive the same digital in-phase or digital quadrature modulationsignal from input 504. In turn, the functional block 506 derives (i.e.,provides) a multi-state switching signal SS3, the state of whichcorresponds to the magnitude of the digital modulation signal receivedfrom input 504.

The circuitry 500 also includes an IQ generator 508 configured toreceive a carrier signal from a local oscillator (not shown; refer to306 of FIG. 3) and to provide an analog in-phase carrier signal and ananalog quadrature carrier signal. The difference between the in-phaseand quadrature carrier signals is referred to as (analog) differentialsignal DS2.

The circuitry 500 also includes a first transistor 510, a secondtransistor 512, and a plurality of selectably switchable current sources(current sources) 514. The transistors 510 and 512 and the plurality ofcurrent sources 514 cooperatively define a digital-to-analog converterDAC3. The DAC3 is configured to convert the multi-state switching signalSS3—which corresponds to the magnitude of the digital modulation signalinput at 504—into a corresponding analog magnitude signal under thecontrolling influence of the differential signal DS2.

Each of the current sources 514 can be configured to provide anysuitable current value. In one non-limiting implementation, all of thecurrent sources 514 are configured to provide a common electricalcurrent value (e.g., 0.01 mA, etc.). In another non-limitingimplementation, the current sources 514 are respectively configured suchthat the overall plurality exhibits constant steps therebetween (e.g.,0.01 mA, 0.02 mA, 0.03 mA . . . , etc.). Other weighting schemes canalso be used (linear weighting, binary weighting, logarithmic weighting,etc.). The current sources 514 may be individually weighted so that,through selective switching, any practical combination of electricalcurrents can be summed at node 516. The selective switching of currentsources 514 to the node 516 is accomplished by way of the multi-stateswitching signal SS3. While three current sources 514 are depicted, itis to be understood that any suitable number of current sources 514 maybe included in accordance with the resolution of the signal conversionto be performed by DAC3.

The circuitry 500 also includes a third transistor 518, a fourthtransistor 520, a fifth transistor 522, and a sixth transistor 524cooperatively configured to define a mixer MIX3. The mixer MIX3 isconfigured to mix the analog magnitude signal provided by DAC3 with thedigital sign signal and inverted digital sign signal provided by block502. The mixer MIX3 then provides the resulting mixed signal to a pairof nodes 526. The nodes 526 are coupled to the source of bias potentialV-BIAS by way of respective resistors 528 and 530. The nodes 526—alsoreferred to as output nodes—are understood to be coupled or coupleableto a driver or other suitable stage (e.g., driver 332 of FIG. 3).

In operation, the circuitry 500 effectively changes the sign of theanalog magnitude signal by cross-switching the paths from the DAC3 tothe nodes 526 by way of the mixer MIX3. This cross-switching isperformed in accordance the instantaneous state of the digital signsignal and the inverted form of the digital sign signal as provided byblock 502. Thus, mixing is substantially achieved by way of selectivelyconnecting or cross-connecting the analog output from DAC3 to the outputnodes 526. In this way, the circuitry 500 handles both positive andnegative polarities of the input modulation signal by way of a singledigital-to-analog conversion stage, DAC3.

The circuitry 500 may be implemented in any number of suitableimplementations. In one non-limiting implementation, some or all of thecircuitry 500 can be implemented as an integrated circuit. In anothernon-limiting implementation, some or all of the circuitry 500 can beimplemented within a 65 nanometer environment. In yet anothernon-limiting implementation, some or all of the circuitry 500 isimplemented via one or more discrete electronic components. Otherimplementations including the circuitry 500, or a portion thereof, canalso be used.

Fourth Illustrative Implementation

FIG. 6 is a block schematic diagram depicting electronic circuitry(i.e., circuitry) 600 in accordance with the present teachings. Onehaving ordinary skill in the pertinent arts can appreciate that otherfunctional elements respectively taught herein and/or known in the artcan be used in combination with the electronic circuitry 600. However,such other functional elements are omitted from FIG. 6 in the interestof clarity of understanding.

The circuitry 600 includes circuitry (i.e., functional block) 602configured to receive either a digital in-phase modulation signal ordigital quadrature modulation signal from input 604. In turn, the block602 derives (i.e., provides) a digital sign signal and an inverted formof the digital sign signal, in accordance with the instantaneouspolarity of the input modulation signal. The circuitry 600 also includesother circuitry (i.e., another functional block) 606 configured toreceive the same digital in-phase or digital quadrature modulationsignal from input 604. In turn, the functional block 606 derives (i.e.,provides) a multi-state switching signal SS4, the state of whichcorresponds to the magnitude of the digital modulation signal receivedfrom input 604.

The circuitry 600 also includes an IQ generator 608 configured toreceive a carrier signal from a local oscillator (not shown; refer to306 of FIG. 3) and to provide an analog in-phase carrier signal and ananalog quadrature carrier signal, the difference between the two signalsbeing referred to as a differential signal DS3.

The circuitry 600 includes a multiplexer (MUX) 610. The MUX 610 isconfigured to receive the analog differential signal DS3 and the digitalsign signal from block 602. The MUX 610 is further configured to providea multiplexed signal MS1. As such, the MUX 610 can be considered to be astate machine having three input signals and one output signal. Thecircuitry 600 also includes another multiplexer (MUX) 612. The MUX 612is configured to receive the analog differential signal DS3 and theinverted form of the digital sign signal from block 602. The MUX 612 isfurther configured to provide a multiplexed signal MS2. As such, the MUX612 can also be considered to be a state machine having three inputsignals and one output signal.

The circuitry 600 also includes a first transistor 614, a secondtransistor 616, and a plurality of selectably switchable current sources(current sources) 618. The transistors 614 and 616 and the plurality ofcurrent sources 618 cooperatively define a digital-to-analog converterDAC4. The DAC4 is configured to convert the multi-state switching signalSS4 into a corresponding analog magnitude signal under the controllinginfluence of the multiplexed signals MS1 and MS2. It is noted that thedigital sign signal and inverted form of the digital sign signals fromblock 602 are included in the multiplexed signals MS1 and MS2. As aresult, effective mixing with the sign and inverted sign signals—inaccordance with their respectively asserted or non-asserted states—isalso accomplished within the DAC4 stage of circuitry 600.

Each of the current sources 618 can be configured to provide anysuitable current value. In one non-limiting implementation, all of thecurrent sources 618 are configured to provide a common electricalcurrent value (e.g., 0.01 mA, etc.). In another non-limitingimplementation, the current sources 618 are respectively configured suchthat the overall plurality exhibits constant steps therebetween (e.g.,0.01 mA, 0.02 mA, 0.03 mA . . . , etc.). Other weighting schemes canalso be used (linear weighting, binary weighting, logarithmic weighting,etc.). The current sources 618 can be individually weighted so that,through selective switching, any practical combination of electricalcurrents can be summed at node 620. The selective switching of currentsources 618 to the node 620 is accomplished by way of the multi-stateswitching signal SS4. While three current sources 618 are depicted, itis to be understood that any suitable number of current sources 618 canbe included in accordance with the resolution of the signal conversionto be performed by DAC4.

The circuitry 600 also includes a third transistor 622 and a fourthtransistor 624. Respective control nodes (i.e., gates) of thetransistors 622 and 624 are coupled to a source of direct current (D.C.)potential VDC. The transistors 622 and 624 cooperatively buffer theanalog signal derived by DAC4 to a pair of output nodes 626. The nodes626 are coupled to a source of bias potential V-BIAS by way ofrespective resistors 628 and 630. The nodes 626, also referred to asoutput nodes, are understood to be coupled or coupleable to a driver orother suitable stage (e.g., driver 332 of FIG. 3).

In operation, the circuitry 600 effectively includes the sign signal,derived from the modulation input signal, within the local oscillator(LO) signal pathway by way of the IQ generator 608 and the MUXs 610 and612. In this way, only one digital-to-analog conversion stage is used(i.e., DAC4), but the timing of the switching (in accordance with theassertion of the sign and inverted sign signals) must be performed asclosely as possible to the zero crossing of the LO signal.

The circuitry 600 can be implemented in any number of suitableimplementations. In one non-limiting implementation, some or all of thecircuitry 600 can be implemented as an integrated circuit. In anothernon-limiting implementation, some or all of the circuitry 600 can beimplemented within a 65 nanometer environment. In yet anothernon-limiting implementation, some or all of the circuitry 600 isimplemented via one or more discrete electronic components. Otherimplementations including the circuitry 600, or a portion thereof, canalso be used.

Illustrative Method

FIG. 7 is a flow diagram 700 depicting a method in accordance with thepresent teachings. The method 700 depicts particular steps in aparticular order of execution. However, certain steps can be omitted orother steps added, and/or other orders of execution can also beperformed, without departing from the scope of the present teachings.The method 700 depicts a flow of distinct and discrete events in theinterest of clarity of understanding. However, one of skill in therelevent arts can appreciate that the method 700 can operate in anessentially continuous manner, such that signals flow smoothly from onestep to the next during processing.

At 702, a digital modulation signal is separated into digital sign anddigital magnitude signals (i.e., derived components). For purposes ofnon-limiting example, it is assumed that a digital in-phase modulationsignal is subject to the described separation, thus resulting in adigital in-phase sign signal and a digital in-phase magnitude signal.Other digital modulation signals, having respectively varyingrelationships to other digital modulations signals, can also be used.

At 704, the digital magnitude signal is converted to an analog magnitudesignal. In one or more implementations, such digital-to-analog (D-to-A)conversion can be performed by way of known means. In one or more otherimplementations, the D-to-A conversion is done by way of particularcircuit means presented herein. For purposes of the ongoing example, itis assumed that analog magnitude signal is derived from the digitalin-phase magnitude signal.

At 706, the analog magnitude signal is mixed with the correspondingdigital sign signal and a differential signal. The differential signalis typically defined by the difference between in-phase carrier andquadrature carrier signals. Thus, both in-phase and quadrature carriersignals can be used in order to realize the differential. However, otherdifferential signals can be used. In another implementation, only theanalog magnitude signal and the digital sign signal are used, and thedifferential signal (or components thereof) is/are not involved in themixing. In any case, a mixed signal is derived.

At 708, the mixed signal from 706 above is added to another mixed signalto derive a summation signal. The other mixed signal can be derived byway of other, simultaneous processing of other signals according to702-706 above. For purposes of ongoing example, it is assumed that ananalog quadrature magnitude signal is mixed with (at least) acorresponding digital quadrature sign signal in order to derive theother mixed signal.

At 710, the summation signal is power amplified and provided to one ormore antennas for broadcast.

Illustrative Device

FIG. 8 illustrates one implementation of a wireless device 800 thatincorporates the circuitry described above with regard to FIGS. 3-6.Wireless device 800 includes a signal processor 802, which may beconnected to processing circuitry 804 or other electronic circuitryassociated with the wireless device 800. The signal processor 802 isoperable to separate a digital modulation signal into a digital signsignal and a digital magnitude signal. A digital-to-analog converter 806converts the digital magnitude signal into an analog magnitude signal. Amixer 808 then mixes at least the analog magnitude signal and thedigital sign signal to provide a mixed signal. An exemplary signalprocessor 802 may include, for example, transmitter 300, circuitry 400,and so forth. Signal processor 802 is shown simplified for illustrationpurposes and may include other components, such as drivers, PLLs, and soforth, for processing and transmitting a modulated signal.

Wireless device 800 may have one or more antennas 810 for sending andreceiving signals 812 to and from one or more communication bases 814using one or more modes. Some exemplary types of modes may include aGlobal System for Mobile communications (GSM) mode, a Universal MobileTelecommunications System (UMTS) mode, a Third Generation PartnershipProject Long Term Evolution (3GPP LTE) mode, a WorldwideInteroperability for Microwave Access (WiMax) mode, a Wireless LocalArea Network (WLAN) mode, a Bluetooth (BT) mode, and so forth.Communication base 814 is shown as a base station 814, such as acellular communications tower; however, it is intended that thecommunication base could additionally or alternatively include asatellite, a wireless access point (WAP), Bluetooth (BT) headset, and/orother commutation device.

The wireless device 800 may be or include a cellular phone, wirelessmedia device, a global positioning system (GPS) receiver, or otherdevice capable of receiving and/or transmitting a radio or otherwireless signal 812. For example, the wireless device 800 may be apersonal digital assistant (PDA), a portable computing device capable ofwireless communication, a media player device, a portable gaming device,a personal computer, a wireless access point (WAP) and/or any othersuitable device.

Conclusion

For the purposes of this disclosure and the claims that follow, theterms “coupled” and “connected” have been used to describe how variouselements interface. Such described interfacing of various elements maybe either direct or indirect. Although the subject matter has beendescribed in language specific to structural features and/ormethodological acts, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features or acts described. Rather, the specific features andacts are disclosed as preferred forms of implementing the claims.

1. An electronic circuit, comprising: circuitry configured to separate adigital modulation signal into a digital sign signal and a digitalmagnitude signal; a digital-to-analog converter configured to convertthe digital magnitude signal into an analog magnitude signal; and amixer configured to mix at least the analog magnitude signal and thedigital sign signal and provide a mixed signal.
 2. The electroniccircuit according to claim 1, wherein the mixer is further configured tomix at least an analog carrier signal with the analog magnitude signaland the digital sign signal to provide the mixed signal.
 3. Theelectronic circuit according to claim 2, further comprising anin-phase-and-quadrature (IQ) generator configured to derive the analogcarrier signal from a local oscillator signal.
 4. The electronic circuitaccording to claim 3, wherein the local oscillator signal corresponds toa carrier signal.
 5. The electronic circuit according to claim 3,wherein: the analog carrier signal is an analog in-phase carrier signal;and the IQ generator is further configured to derive an analogquadrature carrier signal from the local oscillator signal.
 6. Theelectronic circuit according to claim 1, wherein the circuitry is firstcircuitry, the digital modulation signal is a first digital modulationsignal, the digital-to-analog converter is a first digital-to-analogconverter, the mixer is a first mixer, the analog magnitude signal is afirst analog magnitude signal, and mixed signal is a first mixed signal,the electronic circuit further comprising: second circuitry configuredto separate a second digital modulation signal into a digital signsignal and a digital magnitude signal, the digital modulation signal ofthe second digital modulation signal orthogonal to the digitalmodulation signal of the first digital modulation signal; a seconddigital-to-analog converter configured to convert the second digitalmagnitude signal into a second analog magnitude signal; and a secondmixer configured to mix at least the second analog magnitude and thesecond digital sign signal and provide a second mixed signal.
 7. Theelectronic circuit according to claim 6, further comprising addercircuitry configured to sum the mixed signal and the other mixed signaland provide a summation signal.
 8. The electronic circuit according toclaim 7, further comprising driver circuitry configured to: poweramplify the summation signal so as to derive an output signal; andprovide the output signal to at least one antenna.
 9. An electroniccircuit, comprising: a digital-to-analog converter, thedigital-to-analog converter configured to perform responsive to amulti-state switching signal; and a mixer, the mixer coupled to receivesignals from the digital-to-analog converter and to perform responsiveto a digital sign signal and an in-phase-and-quadrature (IQ)differential signal, the mixer coupled to provide a mixed signal to apair of output nodes.
 10. The electronic circuit according to claim 9,further comprising a multiplexer configured to receive a digitalmagnitude signal and an inverted form of the digital sign signal and alogic reference signal and derive the multi-state switching signal therefrom.
 11. The electronic circuit according to claim 9, wherein the IQdifferential signal is defined by the difference between an analogin-phase carrier signal and an analog quadrature carrier signal.
 12. Theelectronic circuit according to claim 9, wherein the digital-to-analogconverter is a first digital-to-analog converter, the multi-stateswitching signal is a first multi-state switching signal, the mixer is afirst mixer, and the mixed signal is a first mixed signal, theelectronic circuit further comprising: a second digital-to-analogconverter configured to perform responsive to a second multi-stateswitching signal and the in-phase-and-quadrature (IQ) differentialsignal; and a second mixer coupled to receive signals from the seconddigital-to-analog converter and to perform responsive to an invertedform of the digital sign signal, the second mixer configured to providea second mixed signal by way of the pair of output nodes.
 13. Theelectronic circuit according to claim 12, further comprising amultiplexer configured to receive the digital magnitude signal and thedigital sign signal and a logic reference signal and derive the othermulti-state switching signal there from.
 14. An electronic circuit,comprising: a digital-to-analog converter, the digital-to-analogconverter configured to perform responsive to a multi-state switchingsignal; and a mixer coupled to receive signals from thedigital-to-analog converter and to perform responsive to a digital signsignal and an inverted form of the digital sign signal and anin-phase-and-quadrature (IQ) differential signal, the mixer configuredto provide a mixed signal by way of a pair of output nodes.
 15. Theelectronic circuit according to claim 14, wherein: the IQ differentialsignal is defined by the difference between an analog in-phase carriersignal and an analog quadrature carrier signal; and the multi-stateswitching signal corresponds to a digital magnitude signal.
 16. Anapparatus, comprising: an antenna; and a signal processor coupled to theantenna, the signal processor configured to: separate a digitalmodulation signal into a digital sign signal and a digital magnitudesignal; convert the digital magnitude signal into an analog magnitudesignal; and mix at least the analog magnitude signal and the digitalsign signal to derive a mixed signal.
 17. The apparatus according toclaim 16, further comprising: an adder configured to sum the mixedsignal with at least one other signal to derive a summation signal; anda driver configured to amplify the summation signal to derive an outputsignal, the output signal being coupled to the antenna.
 18. A method,comprising: separating a digital modulation signal into a digital signsignal and a digital magnitude signal; converting the digital magnitudesignal to an analog magnitude signal; and mixing at least the analogmagnitude signal and the digital sign signal to derive a mixed signal.19. The method according to claim 18, wherein the digital modulationsignal is further defined as a digital in-phase modulation signal, themethod further comprising: separating a digital quadrature modulationsignal into another digital sign signal and another digital magnitudesignal; converting the other digital magnitude signal to another analogmagnitude signal; and mixing at least the other analog magnitude signaland the other digital sign signal to derive another mixed signal. 20.The method according to claim 19, further comprising summing the mixedsignal and the other mixed signal to derive a summation signal.
 21. Themethod according to claim 20, further comprising: power amplifying thesummation signal to derive an output signal; and providing the outputsignal to at least one antenna.
 22. The method according to claim 18,further comprising: generating, responsive to a carrier input signal, anin-phase carrier signal and a quadrature carrier signal, the differencebetween the in-phase signal and the quadrature signal defining an analogdifferential signal; and mixing the analog magnitude signal and thedigital sign signal with at least one of the in-phase carrier signal orthe quadrature carrier signal or the analog differential signal toderive the mixed signal.
 23. The method according to claim 18, furthercomprising: multiplexing the digital magnitude signal with at least oneother signal to derive a multiplexed signal; and performing theconverting the digital magnitude signal to the analog magnitude signalby way of the multiplexed signal.
 24. The method according to claim 18,further comprising: multiplexing the digital sign signal with at leastone other signal to derive a multiplexed signal; and performing theconverting the digital magnitude signal to the analog magnitude signalby way of the multiplexed signal.
 25. The method according to claim 18,further comprising: performing the converting the digital magnitudesignal to the analog magnitude signal by way of a plurality of currentsources selectively switchable in accordance with a multi-stateswitching signal.